The recovery of wind energy has been known for thousands of years.
Utilizing wind power for generating electric current has also been known for a long time, in principle ever since the electric generator saw the light of day.
However wind power has encountered difficulties in successfully competing economically with other energy sources for the production of electric power. The use of wind power for this purpose has long been limited to the supply of local energy and experimental plants. Although the commercial production of electric energy based on wind power has gained ground in recent decades its total production of electric power is still very marginal.
In view of the large amount of energy potentially available from wind power and of the various drawbacks associated with the production of electric power from other types of energy sources, it is imperative to create the prerequisites for increased commercially competitive production of electric power based on wind power.
It is therefore not surprising that may different principles and designs have been proposed for wind turbines. To a great extent efforts have been directed towards designing the actual turbine in the best possible way. However, it is important to consider the whole, i.e. not only the aerodynamics of the turbine, but also the mechanical transmission of movement to the generator, the design of the generator and, most particularly, all interaction between the components in these steps of the energy conversion.
A step forward in this respect is represented by the wind-power plant described in WO99/29025. This describes a wind-power unit in which the generator is provided with a stator winding that permits high induced voltages, up to 50 kV. The generator can thus supply current to the electric supply network is without the use of intermediate transformers. This is possible thanks to the special design of the stator winding in which a conducting core is surrounded by a first layer of semiconducting material. This is surrounded by an insulating layer of solid material, which is surrounded by a second semiconducting layer of semiconducting material. This type of winding in an electric turbo-generator has previously been described in WO97/45924.
The generator described in WO99/29025 enables better total economy in a wind-power unit of otherwise conventional type, i.e. with a turbine having a horizontal shaft, the turbine being of propeller type. This eliminates the need for a transformer. Wind turbines with horizontal shafts are currently almost universal.
Besides these, wind turbines having vertical shafts have also been proposed, e.g. as described in U.S. Pat. No. 6,320,273. However, these have not yet been used commercially and remain at the design stage although a few have been realized as experimental plants.
A decisive reason for wind turbines with vertical shafts not being favoured is that the output cannot be controlled by simply turning the turbine blade. They require the generator to first be provided with overload control or for it to be dimensioned large enough to receive the high outputs. This limitation prevents the energy available in winds of high velocity from being exploited.
Added to other drawbacks such as low ratio between the peripheral speed of the turbine and the wind velocity and low power coefficient, i.e. the ratio between useful power and theoretical wind power, this has meant that turbines with vertical shafts have not hitherto been considered a realistic alternative.
However wind turbines with horizontal shafts also have a number of drawbacks. The generator must either be arranged high up in the mast, in the hub of the turbine, which makes the construction expensive, or an angle gear must be arranged in the hub which also involves expense, as well as incurring losses in efficiency. A conventional wind turbine also requires a device for turning the unit depending on the direction of the wind. With a turbine of propeller type the wind power is fully exploited only in the peripherally outer areas of the turbine and the construction is in principle two-dimensional so that the wind energy is not utilized in its depth direction.
The object of the present invention, in the light of the above, is to endeavour to utilize the advantages associated with a generator with a stator winding of the type described in WO97/45924 in a wind-power unit in such a way that the wind-power unit is simple, inexpensive and capable of generating a relatively large amount of electric energy in relation to the potential available.